/*
* Implements hook_css_alter()
*/
function dranattheme_css_alter_x(&$css) {
// Remove colors.css file.
unset($css[drupal_get_path('theme', 'anat') . '/color/colors.css']);
}

And in client side (jQuery):
http://ianjgough.com/jquery/add-and-remove-stylesheets-with-jquery/
Or
http://stackoverflow.com/questions/7846980/how-do-i-switch-my-css-styles...